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Equipment Discussions >> Reflectors

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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

First Light On My 20" f/3 Lockwood/JP Astrocraft
      #5529511 - 11/20/12 07:25 AM Attachment (872 downloads)

It is amazing how time flies when you order a new telescope. At first is creeps and then later, it slips from your day-to-day consciousness and suddendly it is found to be nearing completion. This has been the case with my 20" f/3 Lockwood/JP Astrocraft scope. In about 3 weeks, it will have gone through the final completion stage.

We did however get first light in Central Illinois this past weekend when I went up to look at the progress and provide further input into some of the design features. It is so feature laden for visual, astrovideo, binoviewing and DSLR applications that I will save that for another post.

The scope has a Lockwood 20" 1.25" thick Pyrex f/3 primary coupled with a 5" m.a. Lockwood secondary. The JPA custom mirror cell was tested by Lockwood under various bench conditions with the unfinished primary and has been optomized for the thin mirror to operate in all positions. The mirror cell is a work of art all by itself with the use of spherical bearings on each triangle and roller bearings on the lower mirror edge supports. Views of Jupiter's GRS and surrounding ovals at 219x under less than ideal conditions still showed very detailed and colorful images. The unfinished podium on the non-viewing side includes wired and wireless handpands, 12" ultrabook computer, power supplies for the computer and eventually a heated shield that will prevent the computer screen from dewing up. All wiring is internally routed and the entire scope will be powered by one external 12v wire going into the powered ground board.

Mike Lockwood, the optician on this project, is a former electrical engineer/research scientist/ATM that went into the optical business and is building what are arguably some of the finest and most consistent sub f/4 optics on the planet in sizes up to 60" and f ratios as fast as f/2 (he recommends no faster than f/2.75 for Newtonians and I have viewed through one of his 28" f/2.75's that was an absolute stunner). John Pratte, the scope builder, is a chemical engineer, manufacturing executive, former world champion NHRA car tuner/builder, optician, machinist and all around nice guy.

I have included a picture that Mike Lockwood took this weekend as we all experienced a group first light.

Edited by Bob S. (11/20/12 02:04 PM)


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tezster
scholastic sledgehammer
*****

Reged: 07/14/09

Loc: Missisauga, Canada
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5529576 - 11/20/12 08:23 AM

That is one FINE looking scope! It's hard to imagine it has the same FL as a 10" F6 - comfy seated observing with feet on the ground all the way to the zenith

Mind if I ask what the maximum EP height is?


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JayinUTModerator
I'm not Sleepy
*****

Reged: 09/19/08

Loc: Utah
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: tezster]
      #5529599 - 11/20/12 08:42 AM

Beautiful scope! Oh the views you are going to have!

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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: tezster]
      #5529620 - 11/20/12 09:02 AM

Quote:

That is one FINE looking scope! It's hard to imagine it has the same FL as a 10" F6 - comfy seated observing with feet on the ground all the way to the zenith

Mind if I ask what the maximum EP height is?




Maximum ep height is 62" at zenith. John Pratte had to add height to the rocker box feet and make a slightly taller rocker box to get the desired height that I wanted.

Edited by Bob S. (11/20/12 09:02 AM)


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Darren Drake
Carpal Tunnel
*****

Reged: 10/09/02

Loc: Chicagoland
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: JayinUT]
      #5529625 - 11/20/12 09:07 AM

Very nice! What is that thingy above the focuser? It looks like another focuser.....

Edited by Darren Drake (11/20/12 09:08 AM)


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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Darren Drake]
      #5529632 - 11/20/12 09:09 AM

Quote:

Very nice! What is that thingy abouve the focuser? It looks like another focuser.....



You can never have enough focusers Actually it is a 1.25"-2" holster for placement of my Mallincam when it is out of the focuser. The 1.25" portion of the holder is a Baader Clic-Lock device that requires just a slight turn of the knurled nob to secure the camera. You are also probably wondering about the turnbuckle on the front of the rockerbox/mirror box. That is used in conjunction with two sliding bolts on the rear of the mirror box that go into the rocker box to place it in an upright position to simply lean the telescope over and wheel it out to my observing site. The axles have quick release pins that allow the wheels to come off and the axle to be removed. However, you can observe with the wheels attached.


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cliff mygatt
Carpal Tunnel


Reged: 01/27/09

Loc: Kitsap County, WA
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5529655 - 11/20/12 09:29 AM

It is a lovely scope combined with great optics, one cannot go wrong. Looking forward to see some of those mallincam photos. Good Luck!

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Busguy
member


Reged: 06/14/07

Loc: Kentucky
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: cliff mygatt]
      #5530279 - 11/20/12 02:16 PM

What a beautiful scope. Craftsmanship looks superb.

Enjoy many nights with it.

Joe


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killdabuddha
Pooh-Bah
*****

Reged: 08/26/11

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Busguy]
      #5530358 - 11/20/12 02:53 PM

Wow. And how in the world did you get those angle-fitted tube-plug mounting plates?

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JimMo
I'd Rather Do It Myself


Reged: 01/08/07

Loc: Under the SE Michigan lightdom...
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5530359 - 11/20/12 02:53 PM

Awesome telescope Bob. I'm sure you'll be thrilled with the views.

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auriga
Pooh-Bah


Reged: 03/02/06

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5530623 - 11/20/12 04:57 PM

Bob,
Congratulations, a superb scope! You will find it easy and enjoyable to use.

I am not at all surprised at how good it is, since I have the 16"f/4 version, the "sweet sixteen' pictured on John Pratte's web site. It's a beauty and a great pleasure to use. I have had no trouble with it at all. Easy to collimate, retains object when I change eyepieces, moves easily but stays where I put it. Very solid construction, very rigid, goes together easily and disassembles easily. I have a Wessling mirror, one of the last ones he made rather than a Lockwood but I think they would be equivalent. I notice you have chosen the same wood stain I did. Looks great.

Let us know your experiences with the 20" f/3 once it is delivered and you have a chance to do some more observing with it. You are one of the most experienced posters with a variety of scopes so it will be good to hear your take on this one.

Bill Meyers


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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: auriga]
      #5530745 - 11/20/12 06:13 PM

Quote:

Bob,
Congratulations, a superb scope! You will find it easy and enjoyable to use.

I am not at all surprised at how good it is, since I have the 16"f/4 version, the "sweet sixteen' pictured on John Pratte's web site. It's a beauty and a great pleasure to use. I have had no trouble with it at all. Easy to collimate, retains object when I change eyepieces, moves easily but stays where I put it. Very solid construction, very rigid, goes together easily and disassembles easily. I have a Wessling mirror, one of the last ones he made rather than a Lockwood but I think they would be equivalent. I notice you have chosen the same wood stain I did. Looks great.

Let us know your experiences with the 20" f/3 once it is delivered and you have a chance to do some more observing with it. You are one of the most experienced posters with a variety of scopes so it will be good to hear your take on this one.

Bill Meyers




Thanks Bill. I too had a 18" f/4.5 Wessling mirror in a beautiful structure whos name escapes me for the moment. It was an absolutely superb mirror. Dick was one of the handful of very good opticians. John Pratte has some of his mirrors and at least one or two for sale I think.

John as you know has been absolutely wonderful to work with. He is extremely meticulous and thinks things through before charging ahead. I could not ask for a better build.
Bob


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Mike Lockwood
Vendor, Lockwood Custom Optics
*****

Reged: 10/01/07

Loc: Usually in my optical shop
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: killdabuddha]
      #5530774 - 11/20/12 06:31 PM

Quote:

Wow. And how in the world did you get those angle-fitted tube-plug mounting plates?



Well, John made them, of course.

While using this scope, I found myself repeatedly asking for the observing chair - my back was hurting from having to stoop over at the eyepiece of what is very clearly a telescope that should be used while seated.


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Jarad
Postmaster
*****

Reged: 04/28/03

Loc: Atlanta, GA
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Mike Lockwood]
      #5530946 - 11/20/12 08:06 PM

Glad to see it finally arrived, Bob! I'm sure you'll enjoy it under those nice steady Florida skies.

Be sure to bring it to PSSG next year!

Jarad


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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Jarad]
      #5530993 - 11/20/12 08:38 PM Attachment (250 downloads)

Quote:

Glad to see it finally arrived, Bob! I'm sure you'll enjoy it under those nice steady Florida skies.

Be sure to bring it to PSSG next year!

Jarad




Jarad, It has not "arrived" yet but is getting within three weeks of arrival.

Here is a picture of the custom-machined billet aluminum offset spider hub, collimation screws, tilt plate and vanes that John Pratte manufactured. You will also notice that the UTA has two flat sides that allow it to nest better in the mirror box if that is desired.

You will also notice that the spider vanes are indeed parallel (opposing vanes) and perpendicular (neighboring
vanes), but they are not coincident, or on the same line.

The purpose of this vane's orientation was to prevent the 5" secondary from experiencing rotational torque generally associated with larger secondaries. You see people using wheel weights to prevent the rotation. John Pratte as an engineer (with the concurrence of Mike Lockwood) couldn't live with that and made them so there is virtually no rotational torquing of the secondary. The diffraction spikes are just four but behave a bit differently when you defocus on a star seperating in a horizontal fashion. The spider vanes also have their own dedicated uprights on the UTA that are primary support for the vanes and secondarily for the UTA rings that have other supports. The vertical slots in the billet center hub are reportedly for receiving transmissions from outer space. I am thinking of also using this as a SETI instrument

Edited by Bob S. (11/20/12 09:06 PM)


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mtb54703
professor emeritus
*****

Reged: 11/12/08

Loc: Eau Claire, WI
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5531870 - 11/21/12 10:20 AM

Quote:


The purpose of this vane's orientation was to prevent the 5" secondary from experiencing rotational torque generally associated with larger secondaries.




Interesting... It's not just that its a larger secondary, it's the greater secondary offset that's required for a faster mirror that is responsible for the greater rotational torque...



Awesomely nice looking scope!


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jim molinari
member
*****

Reged: 02/02/08

Loc: California
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5532428 - 11/21/12 02:54 PM

Bob ...
Very well thought out with top quality optics and structure. I like your Watec Monitor and Mallincam mount ... clever! I will be interested to hear how the cooling/airflow system performs. I hope you get a chance to bring it out West where I can see it in action. Congrats and enjoy!
Jim


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Jarad
Postmaster
*****

Reged: 04/28/03

Loc: Atlanta, GA
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5532454 - 11/21/12 03:12 PM

Quote:

Jarad, It has not "arrived" yet but is getting within three weeks of arrival.




Hey, no fair! You can't title your thread "First light" until you get the scope and get first light!

Now I can't be jealous for 3 more weeks!

Jarad


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David Castillo
Carpal Tunnel
*****

Reged: 09/09/06

Loc: Carmel Valley, Ca
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Jarad]
      #5532499 - 11/21/12 03:33 PM

Looks like the best thing to cure a back ache.
----
Dave


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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: jim molinari]
      #5532572 - 11/21/12 04:13 PM

Quote:

Bob ...
Very well thought out with top quality optics and structure. I like your Watec Monitor and Mallincam mount ... clever! I will be interested to hear how the cooling/airflow system performs. I hope you get a chance to bring it out West where I can see it in action. Congrats and enjoy!
Jim




Jim, The cooling system is a combination of proven technologies used by two different astronomers and many others I am sure. BTW, we sure had some beautiful views through your 20" scope, Chris Ford's 24" and Nick Tsakoyias TEC 180 FL scope at the Golden State Star Party this year. Joe Wambo with his 32" f/3.7 Lockwood/Webster placed a fan above his primary mirror scrubing off the boundary layer. I also talked with Jimmy Lowery who has a 48" f/4 telescope out in Texas and we were discussing cooling strategies for mirrors and he mentioned that he uses 10 Maglev (magnetic levitation) fans in an enclosed rear mirror cell for his behemoth scope.

What John Pratte operationalized was an enclosure for the rear of the telescope that has at the center a Maglev fan (the fans are inherently more vibration free than a conventional motored fan) mounted in Sorbothane and fastened with a sandwiched support plate to the rear aluminum enclosed back. The fan has a potentiometer to control fan speed/air flow and there is an annulus above the primary that creates a venturi effect that sucks the air off the mirror face and out the back of the scope. On the front of the mirror about a foot above the primary will be a smaller Maglev fan suspended by thin but sturdy wires that will also be a variable speed device and blow air away from the center of the mirror. The fan will be able to rotate out of the way to collimate the scope.

The combination of the blowing/sucking system we have termed the Comprehensive Boundary Layer Mitigation System or CBLMS for short. The CBLMS should accomplish several things: 1. It should scrub the boundary layer off the surface of the primary 2. It should provide for more rapid equilibration of the primary and uniformally accomplish this with the combined fan systems. Again, these technologies have been used seperately but to my knowledge not quite in the way that we are going about it.

In Joe Wambo's scope at this years Winter Star Party in the Florida Keys, we were looking at Mars at 950x with "etched" views of the Martian atmosphere and planets surface. We could see very distinctly defined clouds above the Martian surface. Now, my little 20" will not produce those kind of views with eyepieces but it sure will with my Mallincam Extreme astrovideo camera. Bob

Edited by Bob S. (11/21/12 07:27 PM)


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